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Hi Poonam,<br>
<br>
Kim and I discussed this fix and we think it's correct for this
case, but can you move ensure_klass_alive out of Klass and into a
local static function in jvmtiGetLoadedClasses.cpp? We don't want
this to be the normal way to do things in jdk11 but there are
similar local functions in jdk10 and 8 for your backports, so this
would be like those ones.<br>
<br>
Long term, Kim convinced me that Stefan is right and we have to use
the AccessAPI to keep alive class loaders (or holders) when classes
and other things are iterated through the ClassLoaderDataGraph.
I'll make this change at some point soon when I do some other
ClassLoaderDataGraph changes.<br>
<br>
Thanks,<br>
Coleen<br>
<br>
<div class="moz-cite-prefix">On 2/2/18 4:22 PM, Poonam Parhar wrote:<br>
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cite="mid:1f8db89b-f411-c508-7858-e565e1977eb3@oracle.com">
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<p>Adding Coleen to this RFR.<br>
</p>
On 2/2/2018 11:41 AM, Poonam Parhar wrote:<br>
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Hello,<br>
<br>
Please review this fix for a G1GC crash occurring during
concurrent marking.<br>
<br>
Bug: <a class="issue-link" data-issue-key="JDK-8187577"
href="https://bugs.openjdk.java.net/browse/JDK-8187577"
id="key-val" rel="4939883" moz-do-not-send="true">JDK-8187577:</a>
JVM crash during gc doing concurrent marking<br>
Webrev: <a class="moz-txt-link-freetext"
href="http://cr.openjdk.java.net/%7Epoonam/8187577/webrev.00/"
moz-do-not-send="true">http://cr.openjdk.java.net/~poonam/8187577/webrev.00/</a><br>
<br>
Problem:<br>
A klass that has been considered unreachable by G1, can be
looked up in the CLD/SD, and its _java_mirror or _class_loader
can be stored in a root or any other reachable object making it
alive again. Whenever a klass is resurrected in this manner, the
SATB part of G1 needs to be notified about this, otherwise the
concurrent marking remark phase will wrongly unload that klass.<br>
<br>
In this particular crash, while a G1 is doing concurrent marking
and has prepared its list of unreachable classes, JVMTI on a
Java thread traverses classes in the CLD and stores thread-local
JNIHandles for the java_mirror of the loaded classes. G1 does
not have knowledge of these thread-local JNIHandles, and in the
remark phase it unloads classes as per its prior knowledge of
unreachable classes. But when these JNIHandles are later
scanned, it leads to a crash.<br>
<br>
Solution:<br>
Inform G1's SATB that a klass has been resurrected and it should
not be unloaded.<br>
<br>
Testing:<br>
- Customer verification testing<br>
- mach5 jdk-tier1-3, hs-tier1-2<br>
<br>
Thanks,<br>
Poonam<br>
<br>
<br>
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